Method of forming reinforcing yarns or cords

ABSTRACT

Method of making yarns and cords from brittle filaments having a specific modulas greater than 200 X 106 inch. Bundles of brittle filaments are impregnated with a liquid which can subsequently be converted into an elastic solid of high Poissons ratio, the bundles are twisted individually to form yarns or together to form cords and the liquid is converted to the elastic solid, of which the following is a specification.

United States Patent Young Mar. 14, 1972 [54] METHOD OF FORMING REINFORCING YARNS OR CORDS [72] Inventor: Maurice A. Young, Lichfield, England [73] Assignee: Dunlop Holdings Limited, London, En-

gland [22] Filed: July 28, 1969 211 Appl. No.1 848,139

[30] Foreign Application Priority Data Aug. 3, 1968 Great Britain ..37,148/68 [52] U.S.Cl ..57/164,57/153, 161/170 [51] Int Cl ...D02g 3/02, D02g 3/36, C03c 25/02 [58] Field ofSearch ..57/140, 153, 162,164,156, 57/157; 23/2091, 209.1 F; 152/356, 359, 357;

3,358,436 12/1967 Niina et all ..57/153 X 3,391,052 7/1968 Marzocchi ..57/153 X 3,412,062 1l/l968 Johnson et a1. ..23/209.l UX

3,446,003 5/1969 Kolek ..57/153 X 3,447,308 6/1969 Fontijn et al..... ..57/153 X 3,459,585 8/1969 Killmeyer et al. ..57/153 X 3,496,717 2/1970 Costello et a1. ..57/153 X 3,508,874 4/1970 Rulison 23/2094 X 2,817,616 12/1957 Wolfe ..57/153 X 3,301,742 1/1967 Noland et al. ..161/170 3,403,069 9/1968 Benson ..161/170 X Primary Examiner-Donald E. Watkins Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT Method of making yarns and cords from brittle filaments having a specific modulas greater than 200 10 inch. Bundles of brittle filaments are impregnated with a liquid which can subsequently be converted into an elastic solid of high Poissons ratio, the bundles are twisted individually to form yarns or together to form cords and the liquid is converted to the elastic solid, of which the following is a specification.

16 Claims, No Drawings METHOD OF FORMING REINFORCING YARNS OR CORDS This invention relates to reinforcing yarns or cords and particularly to reinforcing yarns or cords for use in dynamic rubber goods.

There are applications in rubber manufacture where reinforcing yarns or cords of high strength and stiffness are required but by virtue of the large amount of flexing which occurs in dynamic rubber products certain other properties are of equal importance. Thus rubber reinforcing yarns or cords must be able to withstand repeated cyclic deformationsdue to tension, compression and shear forces generated within the product.

Many rubber articles are reinforced with yarns or cords of textile materials such as cotton, rayon, nylon. In order to obtain even greater reinforcement it is possible to make cords from mineral based fibers, for example steel, fiberglass and these fibers are also more temperature resistant. Steel, however, is very dense so that its use involves a weight penalty and fiberglass is surface sensitive and prone to fatigue under severe operating conditions.

Fibers composed largely of elemental carbon have recently been developed for reinforcing plastics where their high stiffness to weight ratio and high strength to weight ratio enable them to compete successfully with both fiberglass and steel.

Carbon fibers have high strengths and high moduli but their extensions at break lie in the region 6 percent to less than 0.5 percent.

In multifilament yarns filament migration may occur and thus individual filament lengths may vary over short distances in the yarn. ln yarns of high extensibility materials this is no problem as variations are small in comparison with the breaking extension, but in the case of many carbon/graphite yarns individual filaments may be stressed quite differently during yarn extension and this results in a low strength realization.

According to the present invention a method for the manufacture of a reinforcing yarn comprises impregnating a bundle of brittle filaments with a liquid which can subsequently be converted into an elastic solid having a high Poissons ratio, twisting the bundle of filaments into a yarn and converting the liquid into the elastic solid, the brittle filaments being filaments which have a specific modulus of at least 200x10 inch.

According to the present invention a method for the manufacture of a reinforcing cord comprises impregnating at least two bundles of brittle filaments with a liquid which can subsequently be converted into an elastic solid having a high Poissons ratio, twisting the bundles of filaments together into a cord and converting the liquid into the elastic solid, the brittle filaments being filaments which have a specific modulus of at least 200x10 inch.

According to the present invention also a reinforcing yarn or cord comprises at least one bundle of brittle filaments, the individual filaments having a specific modulus of at least 200Xl inch and each filament being sheathed with an elastic solid of high Poissons ratio.

The brittle filaments are made of material having high strength but low extensibility, for example boron, carbon, graphite. Preferably the filaments have an aspect ratio of at least 100:1.

The specific modulus of a filament is the Youngs modulus of the filament in lb./in. measured parallel to the filament axis, divided by the density of the material in lb./in. Examples of the values of specific moduli of filaments suitable for use in this invention are carbon filaments: 430X to 700 l0 inch, boron filaments: 680x10 inch graphite filaments: 700x10 inch to l,l00 l0 inch.

The liquid impregnant may be converted into the elastic solid in any of a number of ways, for example, cooling chemical cross-linking, the actual method used being of relatively minor importance and depending only on the liquid used.

The elastic solid must have a high Poissons ratio, preferably at least 0.45 measured at tensile strains not greater than 5 percent and it is particularly preferred that the Poissons ratio of the elastic solid is at least 0.48 measured at tensile strains not greater than 5 percent.

Preferably the liquid is a Resorcinol-Formaldehyde-Latex (RFL) adhesive composition. Examples of suitable RFL compositions are (a) an aqueous dispersion of resorcinol-formaldehyde resin, vinyl pyridine rubber, and butadiene rubber and (b) an aqueous dispersion of resorcinol-formaldehyde resin and natural rubber.

Examples of other suitable liquids are solutions of polymers in organic solvents, for example, cis-polyisoprene containing dicumyl peroxide in n-hexane, and liquid polymers, for example liquid polyurethanes.

The impregnated bundle or bundles of filaments may be twisted into a yarn or cord before or after the liquid is converted into the elastic solid or, if the liquid is a composition which is to be dried and then cross-linked, when the composition is dry but before cross-linking has been completed.

The penetration of the liquid into the bundles of filaments during impregnation is substantially complete owing to the lack of twist in the bundles of filaments, and their consequent loose structure. Thus when the liquid is converted to the elastic solid each filaments is sheathed with the elastic solid. The yarns or cords of this invention hence consist of bundles of brittle filaments in which the individual filaments are sheathed with the elastic solid of high Poisson's ratio.

The amount of twist inserted in the yarn or cord depends upon the particular properties desired but in general in a yarn the mean helix angle of the filaments with respect to the axis of the yarn will not exceed 20 and the amount of twist in a cord will not exceed that giving a helix angle of 20 with respect tothe cord axis.

The yarns or cords of the invention have high strength and stiffness and yet are able to withstand the stresses arising in dynamic rubber goods or similar goods of plastics materials such as poly (vinyl chloride). Thus the yarns or cords are suitable, for example, for reinforcing tires, conveyor belts, hose, coated fabrics.

The invention is illustrated by the following Examples Example 1 being included for the purposes of comparison.

EXAMPLE 1 A 19,500 denier cord was made from three bundles of Courtaulds type C (high strength) carbon fiber, the helix angle of the bundles with respect to the cord axis being 13. This cord had a tenacity of 1.8 gm./denier.

EXAMPLE [1 A cord of similar geometry to that of Example I was made from three bundles of carbon filaments as used in Example 1. The bundles of filaments were impregnated with a resorcinolformaldehyde-latex composition having the formulation given in Table l and having a solids content of 28.5 percent.

TABLE 1 parts by weight Resorcinol 0.4 Formaldehyde (37% aqueous solution) 0.7 Gentac Latex (40% solids) 43.0 Pliolite 2104 latex (60% solids) 17.4 Sodium Hydroxide (10% aqueous solution) 0.5 Water 38.0

The impregnant was dried and cured by heating to C. in air for two minutes after the bundles were twisted into the cord.

The resorcinol-formaldehyde-latex composition in cured film form had a Poissons ratio of 0.49 at a strain of5 percent and the cord had a tenacity of 3.7 gm./denier.

EXAMPLE 111 A cord of similar geometry to that of Example 1 was made from three bundles of carbon filaments as used in Example 1. The bundles of filaments were impregnated with 10 percent EXAMPLE IV A cord of similar geometry to that of Example I was made from three bundles of carbon filaments as used in Example I. The bundles of filaments were impregnated with a liquid polyurethane-forming reaction mixture containing a polypropylene glycol/toluene diisocyanate prepolymer and a 1:1 mixture of butane diol and trimethylol propane. The liquid was converted to rubbery polyurethane by heating to 100 C.

for 24 hours after the impregnated bundles were twisted into the cord.

A cured film of the polyurethane rubber had a Poisson's ratio of 0.45 at a strain of 5 percent and the cord had a tenacity of 4.0 gm./denier.

The reinforcing yarn of the present invention may be incorporated in a bead for a pneumatic tire casing. Thus a bead may be made out of several turns of yarn embedded in rubber such that the cross section of the assembly of yarns is approximately square or rectangular.

Alternatively an impregnated bundle or bundles of filaments may be twisted and wound onto a circular former to form a hoop and then the liquid converted into the elastic solid.

Having now described my invention what I claim is:

l. A method for the manufacture of a reinforcing yarn which comprises impregnating a bundle of brittle filaments with a liquid which can subsequently be converted into an elastic solid having a high Poissons ratio, twisting the bundle of filaments into a yarn and converting the liquid into an elastic solid having a Poisson's ratio of at least 0.45 measured at tensile strains not greater than 5 percent, the brittle filaments being filaments which have a specific modulus of at least 200 l 0 inch.

2. A method according to claim 1 in which the brittle filaments are carbon filaments.

3. A method according to claim 1 in which the brittle filaments have an aspect ratio of at least 100:].

4. A method according to claim 1 in which the Poissons ratio of the elastic solid is at least 0.48 measured at tensile strains not greater than 5 percent.

5. A method according to claim 1 in which the liquid is converted to an elastic solid after the brittle filaments are twisted into the yarn.

6. A method according to claim 5 in which the liquid is a cross-linkable polymer composition which is dried before the filaments are twisted into the yarn and cross-linked after the filaments are so twisted.

7. A method according to claim 1 in which the amount of twist inserted into the yarn is such that the mean helix angle of the filaments with respect to the yarn axis is not greater than 20.

8. A method for the manufacture of a reinforcing cord which comprises impregnating at least two bundles of brittle filaments with a liquid which can subsequently be converted into an elastic solid having a high Poissons ratio, twisting the bundles of filaments together into a cord and converting the liquid into an elastic solid having a Poisson's ratio of at least 0.45 measured at tensile strains not greater than 5 percent, the

brittle filaments being filaments which have a specific modulus of at least 20O 10 inch.

9. A method according to claim 8 in which the brittle filaments are carbon filaments.

10. A method according to claim 8 in which the brittle filaments have an aspect ratio of at least :1.

11. A method according to claim 9 in which the Poissons ratio of the elastic solid is at least 0.48 measured at tensile strains not greater than 5 percent.

12. A method according to claim 8 in which the liquid is converted to an elastic solid after the brittle filaments are twisted into the cord.

13. A method according to claim 12 in which the liquid is a cross-linkable polymer composition which is dried before the filaments are twisted into the cord and cross-linked after the filaments are so twisted.

14. A method according to claim 8 in which the amount of twist in the cord is such that the helix angle of the cord is not greater than 20 with respect to the cord axis.

15. A method according to claim 1 in which the brittle filaments are selected from the group consisting of carbon, boron and graphite.

16. A method according to claim 8 in which the brittle filaments are selected from the group consisting of carbon, boron and graphite. 

2. A method according to claim 1 in which the brittle filaments are carbon filaments.
 3. A method according to claim 1 in which the brittle filaments have an aspect ratio of at least 100:1.
 4. A method according to claim 1 in which the Poisson''s ratio of the elastic solid is at least 0.48 measured at tensile strains not greater than 5 percent.
 5. A method according to claim 1 in which the liquid is converted to an elastic solid after the brittle filaments are twisted into the yarn.
 6. A method according to claim 5 in which the liquid is a cross-linkable polymer composition which is dried before the filaments are twisted into the yarn and cross-linked after the filaments are so twisted.
 7. A method according to claim 1 in which the amount of twist inserted into the yarn is such that the mean helix angle of the filaments with respect to the yarn axis is not greater than 20*.
 8. A method for the manufacture of a reinforcing cord which comprises impregnating at least two bundles of brittle filaments with a liquid which can subsequently be converted into an elastic solid having a high Poisson''s ratio, twisting the bundles of filaments together into a cord and converting the liquid into an elastic solid having a Poisson''s ratio of at least 0.45 measured at tensile strains not greater than 5 percent, the brittle filaments being filaments which have a specific modulus of at least 200 X 106 inch.
 9. A method according to claim 8 in which the brittle filaments are carbon filaments.
 10. A method according to claim 8 in which the brittle filaments have an aspect ratio of at least 100:1.
 11. A method according to claim 9 in which the Poisson''s ratio of the elastic solid is at least 0.48 measured at tensile strains not greater than 5 percent.
 12. A method according to claim 8 in which the liquid is converted to an elastic solid after the brittle filaments are twisted into the cord.
 13. A method according to claim 12 in which the liquid is a cross-linkable polymer composition which is dried before the filaments are twisted into the cord and cross-linked after the filaments are so twisted.
 14. A method according to claim 8 in which the amount of twist in the cord is such that the helix angle of the cord is not greater than 20* with respect to the cord axis.
 15. A method according to claim 1 in which the brittle filaments are selected from the group consisting of carbon, boron and graphite.
 16. A method according to claim 8 in which the brittle filaments are selected from the group consisting of carbon, boron and graphite. 